It is estimated that 90% of all machine bearings are lubricated by grease. While oil analysis is a widespread tool for monitoring bearing and lubricated component health of important oil lubricated equipment, grease analysis is not generally adopted in a similar manner for important grease lubricated machines. Analyzing a sample of grease taken from a grease-lubricated bearing is sometimes performed to determine whether the grease has reached the end of its usable life and should be replaced. The ability to adopt regular and routine grease analysis for important grease lubricated machines, however, has been historically limited by the inability to obtain representative samples of the grease and by the complexity of the grease analysis itself.
Pending U.S. patent application Ser. No. 12/107,873 filed by one of the co-applicants herein discloses improved grease sampling devices used to obtain representative samples of grease. This application discloses a method of measuring a quantitative measure of a characteristic material property of grease that can be more easily used to determine the consistency, and thus the health, of used grease.
One known method of measuring a material property of grease is the cone penetration test, ASTM D217. A grease sample is heated and placed below a test cone. The cone drops into the heated grease and the depth of cone penetration is a measure of grease consistency. The cone penetration test requires a large volume sample and is not normally performed on samples of used grease.
Another method of evaluating the consistency of grease is Thermal Gravimetric Analysis (TGA). TGA measures the loss of volatile compounds in a grease sample with increasing temperature. The test is performed in a controlled nitrogen or oxygen atmosphere and requires relatively expensive test equipment.
Thus there is a need for a method of evaluating the consistency of grease that overcomes the problems of the known test methods.